This invention relates to a safety apparatus in a power press machine, which is fitted to the side of a bed of a power press machine on which an operator is positioned, so as to insure safety of the operator.
Press work with a power press machine is extremely dangerous work which might lead to permanent troubles for the operator. Therefore, according to a law, the safety apparatus must be fitted to the power press machine. A ray type, a two-hand operation type and a guard type safety apparatus are typical examples of the safety apparatus of the power press machine, and all of them have been widely used. However, they are not free from the problems inherent thereto and are not yet entirely satisfactory.
The ray type safety apparatus comprises a projector and a light receiver, detects a dangerous state when a part of the body of the operator intercepts the rays of light, and stops the operation of a slide portion. The law stipulates that the safety apparatus must effectively operate through the whole stroke of the slide portion of the press machine, and its fitting position is limited, too.
However, when the ray type safety apparatus is fitted to the fitting position stipulated by the law and the press work is conducted, not only the body of the operator but also a part of his clothes cut off (i.e. interfere with) the rays of light. As a result, the operation of the press machine is stopped, or the operator must be spaced away from the press machine by a predetermined distance to execute the work. In other words, safety is improved at the expense of working efficiency.
Depending on the content of the press work, there is the case where the operator cannot help holding a part of the workpiece with his hand to conduct the press work. In this case, a part of the body of the operator cuts off the rays of light and the ray type safety apparatus starts operating.
Further, when the workpiece is bent, no problem occurs when a flat sheet-like operation is simply bent into an L shape by one bending workpiece, but when the flat sheet-like work is bent around its four sides in the same direction to obtain a box-like shape, the rays of light are sometimes cut off by the portions which have been bent already. Accordingly, depending upon the shape of the product produced by bending the workpiece, the ray type safety apparatus cannot be used in some cases.
As described above, the ray type safety apparatus involves various problems in the actual press operation.
In the two-hand operation type safety apparatus, the slide portion of the press machine cannot be operated unless switches such as push buttons are simultaneously operated by both hands. Moreover, each time one of the hands is removed off from the switch during the operation of the slide portion, the slide portion stops, or the slide portion is caused to stop at each process step. Thus the operation cannot be re-started unless both hands of the operator are removed from the switches for another process step.
To further improve safety, there is a system which combines the two-hand operation type switches with a foot switch. In any case, the bending work cannot be carried out by one operator in the case of bending workpiece in which a part of the work must be gripped by the hand. In this case, the content of the bending work is greatly limited and the working efficiency drops considerably.
The guard type safety apparatus is literally equipped with a guard for preventing the hands of the operator from entering a molding portion of the press machine. The guard is produced in such a manner as to correspond to the shapes of the workpiece and the shaped article, and is fitted to the molding portion. In this system, the guard which has been produced in advance so as to correspond to the workpiece and to the shaped article must be fitted again whenever the workpiece and the shaped article change. Therefore efficiency of the process is low, and the cost of production of the guard also increases overall cost.
For these reasons, various modifications are made by individual users in the ray type and two-hand type safety apparatuses when using them, and these modifications result in a large number of press accidents.